linux-kernel - Re: [PATCH v5 0/2] change the proc handler for nsm_use

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Date:   Wed, 4 Jan 2017 14:35:02 +0800
From:   hejianet <hejianet@...il.com>
To:     linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Serge Hallyn <serge@...lyn.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Kees Cook <keescook@...omium.org>,
        Hugh Dickins <hughd@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Daniel Cashman <dcashman@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <anna.schumaker@...app.com>
Subject: Re: [PATCH v5 0/2] change the proc handler for nsm_use_hostnames

Ping, any comments are welcome. Thanks

B.R.

Jia


On 15/12/2016 3:24 PM, Jia He wrote:
> nsm_use_hostnames is a module parameter and it will be exported to sysctl
> procfs. This is to let user sometimes change it from userspace. But the
> minimal unit for sysctl procfs read/write it sizeof(int).
> In big endian system, the converting from/to  bool to/from int will cause
> error for proc items.
>
> This patch introduces a new proc handler proc_dobool for nsm_use_hostnames.
>
> Changes:
> v5: Fix compilation error when CONFIG_PROC_SYSCTL is not set
> v4: Change (u8 *) to (bool *)
> v3: Introduce a new proc handler proc_dou8vec(suggested by Xinhui Pan)
> v2: Change extern type in lockd.h
>
> The test case I used:
> /***************************************************************/
> #include <linux/kernel.h>
> #include <linux/module.h>
> #include <linux/sysctl.h>
>
> bool __read_mostly nsm_use_hostnames;
> module_param(nsm_use_hostnames, bool, 0644);
>
> static struct ctl_table my_sysctl[] = {
>          {
>                  .procname       = "nsm_use_hostnames",
>                  .data           = &nsm_use_hostnames,
>                  .maxlen         = sizeof(int),
>                  .mode           = 0644,
>                  .proc_handler   = &proc_dointvec,
>          },
>          {}
> };
>
> static struct ctl_table my_root[] = {
>          {
>          .procname       = "mysysctl",
>          .mode           = 0555,
>          .child          = my_sysctl,
>          },
>          {}
> };
>
> static struct ctl_table_header * my_ctl_header;
>
> static int __init sysctl_exam_init(void)
> {
>          my_ctl_header = register_sysctl_table(&my_root);
>          if (my_ctl_header == NULL)
>                  printk("error regiester sysctl");
>
>          return 0;
> }
>
> static void __exit sysctl_exam_exit(void)
> {
>          unregister_sysctl_table(my_ctl_header);
> }
>
> module_init(sysctl_exam_init);
> module_exit(sysctl_exam_exit);
> MODULE_LICENSE("GPL");
> /****************************************************************/
>
> [root@...endian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1
> [root@...endian my]# cat /proc/sys/mysysctl/nsm_use_hostnames
> 16777216
>
> After I change the proc_dointvec to new handler proc_dou8vec with the
> patch:
> [root@...endian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1
> [root@...endian my]# cat /proc/sys/mysysctl/nsm_use_hostnames
> 1
>
> In little endian system, there is no such issue.
> Already tested in both of big and little endian(ppc64 and ppc64le)
>
> Jia He (2):
>    sysctl: introduce new proc handler proc_dobool
>    lockd: change the proc_handler for nsm_use_hostnames
>
>   fs/lockd/svc.c         |  2 +-
>   include/linux/sysctl.h |  2 ++
>   kernel/sysctl.c        | 41 +++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 44 insertions(+), 1 deletion(-)